Efficiency of a turbocharger depends on energy that a turbine receives from exhaust air. Therefore, effects of the turbocharger are small in a low rotation region where the amount of exhaust air from an engine is small. Accordingly, a turbocharging system has been studied, in which a turbocharger and an electric compressor are provided in an air supply path and turbocharging can be performed even in a case where the amount of the exhaust air is small (refer to PTL 1).